Rubber compositions and vulcanizates including comb-branched polymers

ABSTRACT

A vulcanizate comprising a rubber, and a damping component that is prepared by preparing a mixture of living polymers that include living polymers with at least two living ends and living polymers with one living end to form a mixture of living polymers, and coupling the mixture of living polymers with a coupling agent that has at least three reactive functionalities.

[0001] This application gains priority from International ApplicationNo. PCT/US01/25660, filed on Aug. 16, 2001, which gains priority fromU.S. Patent Application No. 60/226,421, filed on Aug. 18, 2000, nowabandoned.

BACKGROUND OF THE INVENTION

[0002] Damping is the absorption of energy, such as vibrational or soundenergy, by a material in contact with the source of that energy. Dampingvibrational energy from a number of sources such as motors and enginescan be desirable.

[0003] Viscoelastic materials are often employed for dampingapplications. Energy is absorbed by the viscoelastic material andconverted into heat. Ideally, viscoelastic materials employed fordamping are effective over a wide range of temperatures and frequencies.

[0004] The viscoelastic nature of materials can be mathematicallyrepresented by the formula G*=G′+iG″ where G* is the complex shearmodulus, G′ is the elastic or storage modulus, G″ is the viscous or lossmodulus, and i={square root}{square root over (−1)}. The dampingeffectiveness of viscoelastic materials can be quantified by measuringviscoelastic response to a periodic stress or strain. Results of dynamicmechanical tests are generally given in terms of G′ and G″, where G″ isdirectly related to the amount of mechanical energy converted to heat,i.e., damping.

[0005] The ratio of G″ to G′ is often referred to as tan δ,${\tan \quad \delta} = \begin{matrix}G^{''} \\G^{\prime}\end{matrix}$

[0006] which quantifies a material's ability to dissipate mechanicalenergy versus the purely elastic storage of mechanical motion during onecycle of oscillatory movement. Tan δ can be measured by a dynamicanalyzer, which can sweep many frequencies at a fixed temperature, thenrepeat that sweep at several other temperatures, followed by thedevelopment of a master curve of tan δ versus frequency by curvealignment. An alternate method measures tan δ at constant frequency overa temperature range.

[0007] In common practice, the tan δ of a material is usually broadenedby taking advantage of the glass transition temperature of severalmaterials within a temperature range. Enhancing hysteresis (tan δ) byusing superposition of glass transition peaks is not desirable becausethe modulus of the material drops dramatically at or about the glasstransition temperature.

[0008] Although numerous compositions are known for damping, there is aneed for improved damping compositions that exhibit a high degree ofdamping over a wide range of temperatures and frequencies withoutinvolving glass transition peaks.

SUMMARY OF THE INVENTION

[0009] In general the present invention provides a vulcanizatecomprising a rubber, and a damping component that is prepared bypreparing a mixture of living polymers that includes, living polymerswith at least two living ends per polymer chain and living polymers withone living end and coupling the mixture of living polymers with acoupling agent that has at least three reactive functionalities.

[0010] The present invention also includes a method for making a dampingcomponent comprising preparing a mixture of living polymers thatincludes living polymers with at least two living ends per polymer chainand living polymers with one living end per polymer chain and couplingthe mixture of living polymers with a coupling agent that has at leastthree reactive functionalities.

[0011] The compositions of the present invention advantageously exhibita high degree of damping, as represented by high tan δ, over a widetemperature range without relying on glass transition peaks. As aresult, superior damping is achieved across a wide temperature rangewithout a deleterious loss in modulus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic drawing of a comb-branched polymer.

[0013]FIG. 2 is a graphical plot of the dynamic moduli sweep of avulcanizate that was compounded with a comb-branched polymer andcompared to a control vulcanizate.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0014] The rubber compositions and vulcanizates of this invention haveimproved damping characteristics because they contain certain polymericmaterials which may also be referred to as “damping materials” that havea high tan δ over a wide temperature and frequency range. Furthermore,these damping materials are viscoelastic and preferably miscible withelastomeric materials.

[0015] The damping materials include comb-branched polymers, which arecomplex and highly branched macromolecular structures. Their exactstructure, however, cannot be defined with any great degree ofcertainty. In general, however, their structure is a distribution ofpolymers having a general topology as illustrated in FIG. 1, i.e., theyare characterized by long-chain branches with smaller side-chainsextending from the longer chains.

[0016] The comb-branched polymers are prepared by preparing a mixture ofliving polymers including living polymers with at least two living ends(DiLi macromonomer) and living polymers with one living end (Limacromonomer), and coupling this mixture of living polymers with acoupling agent that has at least three reactive functionalities. Thiscoupling reaction preferably takes place within an organic solvent. Themain control parameters in synthesizing this class of polymers are themolecular weights of the Li and DiLi macromonomers. During the couplingreaction, the Li macromonomers are coupled to the macromolecule and formthe smaller side-chains, and the DiLi macromonomers are coupled to formthe longer branches.

[0017] The preferred molecular weight of the DiLi and Li macromonomersis best described in terms of their corresponding entanglement molecularweight or length. The entanglement weight or length of a polymer chainrefers to a number of polymer chain repeating (or mer) units thatcorrespond to a molecular weight sufficiently large for entanglements tooccur between molecules of undiluted polymer. This length corresponds toa molecular weight where the slope of a plot of log viscosity vs. logmolecular weight changes from 1.0 to 3.4; the change being associatedwith intermolecular entanglements. In general, the entanglement lengthhas been defined as that length of polymer resulting from about 100 merunits. For purposes of this specification, entanglement length refers toa polymer chain length that includes a number of mer units on the orderof magnitude of 100. For example, the entanglement length forpolystyrene has been experimentally determined to be about 340 merunits, a number that is on the order of magnitude of 100. Additionalexperimental techniques for determining the entanglement length of apolymer are summarized by W. W. Graessley in ADV. POLYM. SCI., Vol. 16,1974.

[0018] DiLi macromonomers preferably have a molecular weight from about0.25 to about 20 times the entanglement molecular weight, morepreferably from about 0.5 to about 10 times the entanglement molecularweight, and even more preferably from about 1 to about 5 times theentanglement molecular weight. The T_(g) of the DiLi macromonomer shouldbe less than −5° C., preferably less than −10° C., and more preferablyless than −15° C.

[0019] Li macromonomers preferably have a molecular weight from about0.25 to 10 times the entanglement molecular weight, more preferably fromabout 0.5 to 5 times the entanglement molecular weight, and even morepreferably from about 1 to about 3 times the entanglement molecularweight. The T_(g) of the Li macromonomer should be less than −5° C.,preferably less than −10° C., and more preferably less than −15° C.

[0020] DiLi macromonomers are preferably synthesized by polymerizingmonomers with a multi-functional polymerization initiators.Anionically-polymerized living polymers are formed by reacting monomersby nucleophilic initiation to form and propagate a polymeric structure.Throughout formation and propagation of the polymer, the polymericstructure is ionic or “living.” A living polymer, therefore, is apolymeric segment having a living or reactive end. For example, when alithium containing initiator is employed to initiate the formation of apolymer, the reaction produces a reactive polymer having a Li atom atits living end. This living end remains after complete polymerization sothat a new batch of monomer subsequently added to the reaction can addto the existing chains and increase the degree of polymerization.

[0021] Li macromonomers are preferably synthesized by polymerizingmonomers with a polymerization initiator. These polymerizations aresimilar to those described for the DiLi macromonomers except for thefact that the initiator is mono-functional.

[0022] For further information respecting anionic polymerization as itrelates to the creation of living polymers with one or more living ends,one can refer to PRINCIPLES OF POLYMERIZATION, 3^(RD) EDITION, by GeorgeOdian, John Wiley & Sons, Inc. (1991), Chapter 5, entitled Ionic ChainPolymerization, or Panek et al., J. AM. CHEM. SOC., 94, 8768 (1972).

[0023] Monomers that can be employed in preparing the living polymersinclude any monomer capable of being polymerized according to anionicpolymerization techniques. These monomers include those that lead to theformation of elastomeric homopolymers or copolymers. Suitable monomersinclude, without limitation, conjugated C₄-C₁₂ dienes, C₈-C₁₈ monovinylaromatic monomers, and C₆-C₂₀ trienes. Examples of conjugated dienemonomers include, without limitation, 1,3-butadiene, isoprene,1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and 1,3-hexadiene. Anon-limiting example of trienes includes myrcene. Aromatic vinylmonomers include, without limitation, styrene, α-methyl styrene,p-methylstyrene, and vinylnaphthalene. When preparing elastomericcopolymers, such as those containing conjugated diene monomers andaromatic vinyl monomers, the conjugated diene monomers and aromaticvinyl monomers are normally used at a ratio of 95:5 to 50:50, andpreferably 95:5 to 65:35.

[0024] Anionic polymerizations are typically conducted in a polar ornon-polar solvent such as tetrahydrofuran (THF) or a hydrocarbon such asthe various cyclic and acyclic hexanes, heptanes, octanes, pentanes,their alkylated derivatives, and mixtures thereof. To promoterandomization in copolymerization and to control vinyl content, a polarcoordinator may be added to the polymerization ingredients. The amountof polar coordinator employed can range between 0 and about 90 or moreequivalents per equivalent of Li. The amount depends on the amount ofvinyl desired, the level of comonomer employed, and the temperature ofthe polymerization, as well as the nature of the specific polarcoordinator (modifier) employed. Suitable polymerization modifiersinclude, for example, ethers or amines to provide the desiredmicrostructure and randomization.

[0025] Multi-functional lithium-containing initiators are employed tocreate the DiLi macromonomer. These multi-functional initiators includecompounds that contain at least two alkyl-lithium, amino-lithium, orbenzyl-lithium functionalities. Multi-functional magnesium-containingand sodium-containing initiators can be substituted for the alkyllithiuminitiators under certain conditions, and therefore reference tomulti-functional initiators herein refers also to all anionicpolymerization initiators that have at least two polymerization cites.

[0026] The preparation of multi-functional lithium-containing initiatorsis well known as described in numerous patents such as U.S. Pat. Nos.5,750,055, 4,205,016, 4,196,154, 3,668,263, 3,663,634, and 3,652,516,which are incorporated herein by reference.

[0027] A preferred method for preparing a multi-functionallithium-containing initiator includes reacting 2 mmol ofsec-butyllithium with 1 mmol of 1,3-diisopropenylbenzene in the presenceof 2 moles of triethylamine. Li-alkoxides can optionally be used topromote a more equal initiation when dissimilar initiators are employed.

[0028] Mono-functional, lithium-containing initiators are employed tocreate the Li macromonomer. Exemplary initiators include, but are notlimited to, alkyl lithium initiators such as n-butyl lithium,arenyllithium initiators, arenylsodium initiators, N-lithiumdihydro-carbon amides, aminoalkyllithiums, alkyl tin lithiums, dialkylmagnesiums, alkyl magnesium halides, diaryl magnesiums, and arylmagnesium halides. Other useful initiators includeN-lithiohexamethyleneimide, N-lithiopyrrolidinide, andN-lithiododecamethyleneimide, as well as organolithium compounds such assubstituted aldimines, substituted ketimines, and substituted secondaryamines. Exemplary initiators are also described in the following U.S.Pat. Nos. 5,332,810, 5,329,005, 5,578,542, 5,393,721, 5,698,646,5,491,230, 5,521,309, 5,496,940, 5,574,109, and 5,786,441.

[0029] The living polymer mixture may be prepared by several methods. Inone method, the DiLi and Li macromonomers are prepared in separatesolutions, and then the solutions are combined. In a second method, theDiLi and Li macromonomers can be prepared sequentially within the samesolution. For example, the DiLi macromonomers can be synthesized, andthen, once this synthesis is complete, the Li macromonomers can beprepared within the same solution by adding monomers and mono-functionalinitiators. Alternatively, the Li macromonomers can be prepared firstfollowed by the preparation of the DiLi macromonomers.

[0030] In a third method, the living polymers can be preparedsimultaneously. In this synthesis, a solution of the mono-functional,lithium-containing initiator and multi-functional lithium-containinginitiator is prepared, and then monomer is added to this solution.

[0031] To the living polymer mixture is added a coupling agent having atleast three reactive functionalities. Coupling agents can be added via asingle charge at the completion of the polymerization of the monomers.Alternatively, they can be added in increments as two or more charges.Alternatively, coupling agents can be added continuously over a periodof time, for example, five minutes to two hours. Incremental orcontinuous addition of the coupling agent is preferred to promote amaximum degree of coupling without overshooting the optimum level ofcoupling, which may cause gelation of the polymer in the reactor.

[0032] In one embodiment, the coupling agent can be defined by theformula

(R₁)_(e)−U−(Q)_(f)

[0033] where U is tin or silicon, each R₁, which may be the same ordifferent, is an alkyl having from 1 to about 20 carbon atoms, acycloalkyl having from about 3 to about 20 carbon atoms, an aryl havingfrom 6 to about 20 carbon atoms, or an aralkyl having from about 7 toabout 20 carbon atoms, each Q, which may be the same or different, ischlorine or bromine, e is an integer from 0 to 1,f is an integer from 3to 4, and the sum of e and f is 4. Specific examples of coupling agentsthat can be defined by the foregoing formula include MeSiCl₃, SiCl₄. Inanother embodiment, the coupling agent is tin tetrachloride or R₂SnCl₃,where R₂ is an alkyl, cycloalkyl or aralkyl having from 1 to about 12carbon atoms, or mixtures thereof. Exemplary coupling agents of thisembodiment include may tri-functional and higher coupling agents, whichare well known, such as MeSiCl₃, trichlorotoluene, dioctylphthalate, andthe like.

[0034] When employing a tri-functional coupling agent, the molar ratioof the DiLi macromonomer to the Li macromonomer to the coupling agent ispreferably about 0.5-1.5:0.5-1.5:0.5-1.5 and most preferably 1:1:1.

[0035] When a tetra-functional coupling agent is employed, the molarratio of DiLi macromonomer to the Li macromonomer to the coupling agentis preferably 0.5-1.5:1-4:0.5-1.5 and most preferably 1:2:1. As thenumber of reactive functionalities or the coupling agent increases, theamount of Li macromonomer in relation to the other components increases.

[0036] Preferably, the damping materials have a tan δ greater than 0.35at temperatures from about −40° to about 120° C. In this temperaturerange, the tan δ of the damping materials are more preferably greaterthan 0.5, and even more preferably greater than 0.8. The dampingmaterials are also preferably viscoelastic and therefore has a T_(g)less than −5° C., more preferably less than −20° C., and even morepreferably less than −30° C.

[0037] The damping materials are employed in rubber compositions orvulcanizates. More particularly, the rubber compositions andvulcanizates of this invention include from about 1 to about 500,preferably from about 5 to 300, and more preferably from 15 to about100, parts by weight of the damping materials per 100 parts by weightrubber (phr).

[0038] The rubber to which the damping materials can be added may bereferred to as a binder or matrix. The morphology of the rubbercompositions and vulcanizates, however, are not limited to co-continuousphases, i.e., homogeneous blends, or discrete phases within a matrix orbinder, i.e., heterogeneous blends. Preferably, the rubber compositionsand vulcanizates of this invention are homogeneous to the extent thatdiscrete phases are not visible when using light scattering techniques.

[0039] Many elastomeric materials, both natural and synthetic, can beused as the binder. These elastomers include, without limitation,natural rubber, synthetic polyisoprene rubber, styrene/butadiene rubber(SBR), polybutadiene, butyl rubber, neoprene, ethylene/propylene rubber,ethylene/propylene/diene rubber (EPDM), acrylonitrile/butadiene rubber(NBR), silicone rubber, fluoroelastomers, ethylene/acrylic rubber,ethylene/vinyl acetate copolymers (EVA) epichlorohydrin rubbers,chlorinated polyethylene rubber, chlorosulfonated polyethylene rubbers,hydrogenated nitrile rubber, tetrafluoroethylene/propylene rubber,polyurethane, and mixtures thereof. As used herein, the term elastomermay refer to a blend of synthetic and natural rubber, a blend of varioussynthetic elastomers, or simply one type of elastomer. The elastomersmay also include functionalized elastomers.

[0040] Other components that may be added to the elastomeric binder ormatrix include reinforcing fillers, plasticizers, antioxidants,processing aids, and dyes. Exemplary fillers include carbon black,silica, mineral fillers such as clays, including hard clays, soft clays,and chemically modified clays, mica, talc (magnesium silicate), CaCO₃,TiO₂, Mg(OH)₂, ground coal, ground and/or reclaimed rubber, aluminatrihydrate, and mixtures thereof.

[0041] The damping materials can be blended with a rubber composition byusing several techniques. For example, the damping materials may bepre-blended with the rubber composition, and then the pre-blend ormasterbatch can be compounded with optional fillers, vulcanizing agents,and other rubber additives. Alternatively, the damping materials may beadded directly to a rubber composition that includes at least oneelastomer and other optional rubber additives including fillers andvulcanizing agents. This mixing or blending can be performed in a millor internal mixer. Alternatively, the damping materials can be blendedinto the elastomeric binder while in solution. For example, the dampingmaterials and polymeric matrix can be dissolved in a solvent and thesolution subsequently blended. The solvent is then evaporated, leavingbehind the elastomer-damping additive mixture.

[0042] Once the damping material is added, the elastomeric matrix may becured or vulcanized by using conventional techniques. Conventionalvulcanization typically includes the use of vulcanizing agents in anamount from about 0.5 to about 4 phr. For example, sulfur orperoxide-based curing systems may be employed. The cured elastomericbinder, which includes a damping materials and optional other additives,may be referred to as a rubber product, vulcanizate, or simply rubber.Depending on the nature of the damping material, the damping materialmay become incorporated into the crosslinked network of the curedelastomeric matrix.

[0043] In one embodiment, the damping material is added to avulcanizable composition that is useful for making tire rubber. Here,the damping material is added in an amount from about 1 to about 1,000,more preferably 1 to about 300 and even more preferably about 1 to about60, pbw phr. The addition of the damping material improves the overalltraction of tire rubber including wet traction, snow traction, and drytraction. Advantageously, the wet traction of tire rubber, whichpredicted by hysteresis loss at 0° C., and snow traction, which ispredicted by hysteresis loss at −20° C., can be improved.

[0044] Although damping materials are added to vulcanizable compositionsthat are useful for fabricating tire rubber, practice of this inventiondoes not alter the type or amount of other ingredients, and thereforepractice of this invention is not limited to any one vulcanizablecomposition of matter or tire compounding stock.

[0045] Tire formulations include an elastomer or base rubber componentthat is blended with reinforcing fillers and at least one vulcanizingagent. These compositions typically also include other compoundingadditives such as accelerators, oils, waxes, scorch inhibiting agents,and processing aids. Compositions containing synthetic rubbers typicallyinclude antidegradants, processing oils, zinc oxide, optional tackifyingresins, optional reinforcing resins, optional fatty acids, optionalpeptizers, and optional scorch inhibiting agents.

[0046] Both synthetic and natural elastomers are employed within tireformulations. These elastomers include, without limitation, naturalrubber, synthetic polyisoprene, poly(styrene-co-butadiene),polybutadiene, and poly(styrene-co-butadiene-co-isoprene).

[0047] Reinforcing agents, such as carbon black or silica, are typicallyemployed from about 1 to about 100, preferably about 20 to about 80, andmore preferably about 40 to about 80, pbw phr.

[0048] Typically, a coupling agent is added when silica is used. Onecoupling agent conventionally used is bis-[3(triethoxysilyl)propyl]-tetrasulfide, which is commercially available under thetradename SI69 (Degussa, Inc.; New York, N.Y.).

[0049] Reinforced rubber compounds can be cured in a conventional mannerwith known vulcanizing agents. For example, sulfur or peroxide-basedcuring systems may be employed. For a general disclosure of suitablevulcanizing agents one can refer to Kirk-Othmer, ENCYCLOPEDIA OFCHEMICAL TECHNOLOGY, 3^(rd) Edition, Wiley Interscience, N.Y. 1982, Vol.20, pp. 365-468, particularly VULCANIZATION AGENTS AND AUXILIARYMATERIALS pp. 390-402, or Vulcanization by A. Y. Coran, ENCYCLOPEDIA OFPOLYMER SCIENCE AND ENGINEERING, 2^(nd) Edition, John Wiley & Sons,Inc., 1989. Vulcanizing agents may be used alone or in combination. Thisinvention does not appreciably affect cure times. Typically,vulcanization is effected by heating the vulcanizable composition; e.g.,it is heated to about 170° C.

[0050] Tire formulations are compounded by using mixing equipment andprocedures conventionally employed in the art. Preferably, an initialmasterbatch is prepared that includes the elastomer component and thereinforcing fillers, as well as other optional additives such asprocessing oil and antioxidants. The damping component is preferablyadded during preparation of the initial masterbatch. Once this initialmasterbatch is prepared, the vulcanizing agents are blended into thecomposition. The composition can then be manufactured into tirecomponents by using standard construction and curing techniques. Rubbercompounding and tire construction is known and disclosed in TheCompounding and Vulcanization of Rubber, by Stevens in RUBBER TECHNOLOGY2D EDITION (1973). Pneumatic tires can be manufactured according to U.S.Pat. Nos. 5,866,171; 5,876,527; 5,931,211; and 5,971,046, which areincorporated herein by reference.

[0051] Tire components of this invention preferably include tire treads.The composition can also be used to form other elastomeric tirecomponents such as subtreads, black sidewalls, body ply skims, beadfillers and the like.

[0052] In other embodiments, damping materials are added to elastomericcompositions that are useful for fabricating vibration restrainingmaterials, which are useful as connecting materials such as sealingmaterials, packing, gaskets and grommets, supporting materials such asmounts, holders and insulators, and cushion materials such as stoppers,cushions, and bumpers. These materials may also be used in householdelectrical appliances that produce vibration or noise. For example,these materials could be used in air-conditioners, laundry machines,refrigerators, electric fans, vacuums, driers, printers and ventilatorfans. Further, these materials are also suitable for impact absorbing ordamping materials in audio equipment and electronic or electricalequipment. For example, these materials could be used in compact discplayers including portable units and those within vehicles, videocassette recorders, radio cassette recorders, microphones, insulatorsfor disc drives within computers, various holders for optical discreaders, microphones, or speakers including those within portable andcellular telephones. Still further, these materials are useful insporting goods and shoes.

[0053] In order to demonstrate the practice of the present invention,the following examples have been prepared and tested as described in theGeneral Experimentation Section disclosed hereinbelow. The examplesshould not, however, be viewed as limiting the scope of the invention.The claims will serve to define the invention.

EXAMPLES

[0054] Sample 1

[0055] A 32 oz. Crown-capped bottle, dried and N₂ flushed, was chargedwith hexane (50 g), 1,3-butadiene in hexane (102 g of a 28.3% solution),and 5.0 mmol of a multi-functional lithium initiator. Polymerization wasallowed to proceed for three hours at room temperature, and thenn-butyllithium (5.25 mmol) and 1,3-butadiene in hexane (101 g of a 28.3%solution) were then charged to the bottle. After polymerizing 16 hoursat 30° C., MeSiCl₃ (2.0 mmol) was charged to the bottle.

[0056] Based on the charged components, the calculated M_(n) betweenbranches is 9,500 and the M_(n) of the side branch is 1,900. The SEC(size exclusion chromatography) analysis gave the following:M_(n)=8,500, M_(w)=42,800, and M_(z)=291,200 by using a polystyrenestandard.

[0057] The multi-functional lithium-containing initiators employedthroughout this experimental section was prepared and used within 7 daysof synthesis. The initiator was prepared by reacting sec-butyl lithium(60 mmol) with 1,3-diisopropenylbenzene (30 mmol) in the presence oftriethyl amine (60 mmol) within a N₂ purged bottle at 50° C. for 2hours.

[0058] Sample 2

[0059] A 32 oz. Crown-capped bottle, dried and N₂ flushed, was chargedwith hexane (50 g), 1,3-butadiene in hexane (102 g of a 28.3% solution)and 6.0 mmol of a multi-functional lithium initiator. Polymerization wasallowed to proceed for three hours at room temperature. n-butyllithium(7.0 mmol) and 1,3-butadiene in hexane (102 g of a 28.3% solution) werethen charged to the bottle. After polymerizing 16 hours at 30° C.,MeSiCl₃ (4.0 mmol) was charged to the bottle.

[0060] Based on the charged components, the calculated M_(n) betweenbranches is 7,900 and the M_(n) of the side branch is 1,500. The SECanalysis gave the following: M_(n)=8,400, M_(w)=48,300, andM_(z)=291,200.

[0061] Sample 3

[0062] A 1-gallon stainless steel reactor was conditioned with an-butyllithium/hexane rinse under N₂ purge. 1,3-butadiene in hexane (1.0lbs of a 27.5% solution), multi-functional lithium initiator (54.4mmol), and n-butyllithium (60 mmol) were charged to the reactor withstirring. The temperature was set to 50° C., and an exotherm resulted ina maximum temperature of 80° C. After 2 hours, a sample was taken:M_(n)=4,000, M_(w)=4,300, and M_(z)=4,700. MeSiCl₃ (55 mmol) was thencharged to the reactor in 5 increments. By SEC, it was calculated that97% of starting polymer was coupled by the MeSiCl₃, and the finalproduct was characterized as follows: M_(n)=30,600, M_(w)=115,400, andM_(z)=520,800.

[0063] Sample 4

[0064] A 1-gallon stainless steel reactor was conditioned with an-butyllithium/hexane rinse under N₂ purge. 1,3-butadiene in hexane (3.0lbs of a 27.5% solution), styrene/hex (1.0 lb of a 33% solution),multi-functional lithium initiator (54.4 mmol), n-butyllithium (60mmol), and 50 mmol of the chelating modifier 2,2-di(oxolanyl)propanewere charged to the reactor with stirring. The temperature was set to50° C., and an exotherm resulted in a maximum temperature of 70° C.After 2 hours, a sample was taken: M_(n)=3,800, M_(w)=4,200, andM_(z)=4,600. MeSiCl₃ (51.3 mmol) was charged to the reactor in 4increments. After 30 minutes, diphenylSiCl₂ (7.5 mmol) was added. By SECit was calculated that 99% of the starting polymer was coupled. FinalM_(n)=20,600, M_(w)=124,900, M_(z)=575,400. By 'H NMR, the polymercontained 32.4% styrene and 62.2% of butadiene was in the form of vinylunites. By DSC, the T_(g)=−19° C.

[0065] Samples 5-7

[0066] A 1-gallon stainless steel reactor was conditioned with an-butyllithium/hexane rinse under N₂ purge. As shown in Table I, a firstcharge of 1,3-butadiene in hexane, styrene/hexane, modifier, andn-butyllithium were allowed to react, followed by a second charge ofmonomers and a multi-functional lithium initiator. When polymerizationwas complete, MeSiCl₃ was added to couple the live ends. The ingredientsemployed in the three samples, their addition order, and thecharacteristics of the resulting polymers are shown in Table I. TABLE ISample 5 6 7 Step 1 33% STY/HEX (g) 200 191 275 2.75 1,3 BD/HEX (g) 908908 1339 nBuLi mmol 82 82 92 Modifier mmol 12.0 12.0 12.0 Time (hr.) 2 22 Temperature (°C) 20 20 70 Step 2 33% STY/HEX (g) 182 191 76 27.5% 1,3BD/HEX (g) 908 908 363 DiLi mmol 39 71 80 Time (hr.) 2 2 2 Temperature(°C) 20 30 50 M_(n) (SEC) 3,600 2,900 700;4,700 (BIMODAL) M_(w) 4,7004,100 800;5,100 (BIMODAL) M_(z) 5,400 4,900 950;5,500 (BIMODAL) Step 3MeSiCl₃ mmol 39 76 84 SiCl₄ mmol 10 0.0 0.0 M_(n) (SEC) 14,400 14,10012,800 M_(w) 1,535,200 34,600 34,600 M_(z) 210,164,100 269,400 285,100Tg (°C) (DSC) −28 −35 −54 % Styrene (NMR) 23.3 23.8 22.4 % 1,2 (BD =100) 61.6 58.2 45.0

[0067] Samples 8-9

[0068] A 1-gallon stainless steel reactor is conditioned with an-butyllithium/hexane rinse under N₂ purge. As shown in Table II, asingle charge of 1,3-butadiene in hexane, modifier, a multi-functionallithium initiator, and n-butyllithium were allowed to react. Whenpolymerization was complete, MeSiCl₃ was added in four increments tocouple the live ends. The ingredients employed in two samples, as wellas the characteristics of the resulting polymers, are shown in Table II.TABLE II Sample 8 9 33% HEX (g) 454 454 21.8% 1,3 BD/HEX (g) 1544 1725DiLi mmol 54.4 54.4 nBuLi mmol 59.2 57.6 Modifier mmol 32 30 Time (hr.)1 1 Temperature (°C) 60 70 MeSiCl₃ mmol 42 42 M_(n) (SEC) 19,300 20,500M_(w) 105,700 71,600 M_(z) 554,500 318,100 Tg (°C) (DSC) −17 −21 %Styrene (NMR) 34.2 31.1 % 1,2 (BD = 100) 62.3 56.1

[0069] Samples 10-15

[0070] The comb-branched polymer polymers of Sample 9 were compounded toform Samples 11-15, respectively. The polymers of Sample 9 have a widemolecular weight distribution, which was composed of a high molecularweight and low molecular weight portion. With an M_(n) of 40,000 as thecut-off molecular weight, the comb-branched polymer was composed of 65%low molecular weight and 35% high molecular weight components. InSamples 11-15, the comb-branched polymer systematically replaced thematrix polymer and the SBR oil. Sample 10 was a control. The compoundingrecipe is set forth in Table III. TABLE III Sample 10 11 12 13 14 15 SBR100 96 92 88 84 80 SBR Oil 35 29 23 17 11 5 Comb-Branch Polymer 0 10 2030 40 50 Carbon Black 75 75 75 75 75 75 Antioxidant 1 1 1 1 1 StearicAcid 2 2 2 2 2 2 Diphenylguanimide (DPG) 0.2 0.2 0.2 0.2 0.2 0.2Benzothiazyl Disulfide 0.5 0.5 0.5 0.5 0.5 0.5 Zinc Oxide 2 2 2 2 2 2Sulfur 1.3 1.3 1.3 1.3 1.3 1.3

[0071] The SBR poly(styrene-co-butadiene) was a solution polymerizedcopolymer obtained under the tradename DURADENE™ (Firestone SyntheticPolymers; Akron, Ohio), and the SBR oil was a low molecular weightpoly(styrene-co-butadiene) having an M_(n) of about 10,000, which wasobtained under the tradename RICON OIL 100™ (Ricon, Resins, Inc.; GrandJunction, Colo.).

[0072] An initial mixture was prepared in a 65 gram Banbury mixeroperating at about 60 rpm and an initial temperature of about 80° C.First, the poly(styrene-co-butadiene), stearic acid, and antioxidantwere placed in the mixer, and after about 1.5 minutes, the carbon blackand the SBR oil and comb-branched polymer were added as applicable.Mixing was continued for about 15 minutes, at which time the temperaturewas about 110-115° C. This initial mixture was transferred to a milloperating at a temperature of about 60° C., where it was sheeted andsubsequently cooled to room temperature. The final compound was mixedwithin a Banbury mixer operating at about 60 rpm with an initialtemperature of about 75° C. The compound was removed from the mixerafter about 3 minutes when the material temperature was about 105-110°C. The final compounds were sheeted, formed into shapes, and cured atabout 171° C. for about 15 minutes in standard molds placed in a hotpress.

[0073] The cured samples were analyzed for tensile properties accordingto ASTM D412 at 23° C. These results are provided in Table IV along withdynamic moduli data. The dynamic moduli sweeps for Samples 10 and 15 areshown in FIG. 2. Although the compound T_(g) has declined byincorporation of the comb-branched polymer, the hysteresis of thematerial, particularly at higher strains and temperatures, is increased.This is opposite to standard practice whereby increasing T_(g), onewould attempt to increase hysteresis and visa versa. TABLE IV Com- Tan δ(0 C., Tan δ (25 Tan δ (50 Tan δ (75 Modulus Modulus Modulus Elongationpound 0.5/10% C., 0.5% C., 0.5/10% C., 0.5% (100%) (300%) at Break atBreak Sample T_(g) Strain) Strain) Strain) Strain) [psi] [psi] [psi] (%)10 −17.5 0.49/0.54 0.25 0.24/0.25 0.23 284 929 1841 568 11 −17.20.50/0.54 0.26 0.27/0.25 0.25 322 1002 1796 539 12 −17.0 0.49/0.54 0.270.27/0.26 0.25 306 936 1625 517 13 −16.5 0.50/0.56 0.27 0.28/0.26 0.26349 1047 1705 500 14 −16.1 0.50/0.56 0.27 0.27/0.27 0.26 340 997 1582490 15 −15.6 0.50/0.57 0.27 0.27/0.27 0.26 383 1182 1678 425

[0074] Various modifications and alterations that do not depart from thescope and spirit of this invention will become apparent to those skilledin the art. This invention is not to be duly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A vulcanizate comprising: a vulcanized rubber;and a comb-branched polymer that is prepared by preparing a mixture ofliving polymers that include living polymers with two living ends andliving polymers with one living end to form a mixture of livingpolymers, and adding a coupling agent to the mixture of living polymers,where the coupling agent has at least three reactive functionalities. 2.The vulcanizate of claim 1, where the living polymers derive fromconjugated diene monomers and, optionally, vinyl aromatic monomers. 3.The vulcanizate of claim 1, where the coupling agent has three reactivefunctionalities, and where after said step of adding a coupling agent,the molar ratio of living polymers with two living ends to livingpolymers with one living end to coupling agent is0.5-1.5:0.5-1.5:0.5-1.5.
 4. The vulcanizate of claim 1, where thecoupling agent has four reactive functionalities, and where after saidstep of adding a coupling agent, the molar ratio of living polymers withtwo living ends to living polymers with one living end to coupling agentis 0.5-1.5:1-4.0:0.5-1.5.
 5. The vulcanizate of claim 1, where themixture of living polymers is prepared in a solvent.
 6. The vulcanizateof claim 1, where the living polymer with one living end has a molecularweight from about 0.25 to 10 times the entanglement molecular weight,and where the living polymer with two living ends has a molecular weightfrom about 0.25 to 20 times the entanglement molecular weight.
 7. Thevulcanizate of claim 1, where the living polymer with one living end hasa molecular weight from about 1 to 3 times the entanglement molecularweight, and where the living polymer with two living ends has amolecular weight from about 1 to 5 times the entanglement molecularweight.
 8. The vulcanizate of claim 1, where the comb-branched polymeris present in an amount from about 1 to about 300 parts by weight per100 parts by weight rubber.
 9. A comb-branched polymer prepared by aprocess comprising: preparing a mixture of living polymers that includespolymers having one living end and polymers having two living ends, andadding a coupling agent to the mixture, where the coupling agent has atleast three reactive functionalities.
 10. The polymer of claim 9, wherethe living polymers derive from conjugated diene monomers and,optionally, vinyl aromatic monomers.
 11. The polymer of claim 9, wherethe coupling agent has three reactive functionalities, and where aftersaid step of adding a coupling agent, the molar ratio of living polymerswith two living ends to living polymers with one living end to couplingagent is 0.5-1.5:0.5-1.5:0.5-1.5.
 12. The polymer of claim 9, where thecoupling agent has four reactive functionalities, and where after saidstep of adding a coupling agent, the molar ratio of living polymers withtwo living ends to living polymers with one living end to coupling agentis 0.5-1.5:1-4.0:0.5-1.5.
 13. The polymer of claim 9, where the mixtureof living polymers is prepared in a solvent.
 14. The polymer of claim 9,where the living polymer with one living end has a molecular weight fromabout 0.25 to 10 times the entanglement molecular weight, and where theliving polymer with two living ends has a molecular weight from about0.25 to 20 times the entanglement molecular weight.
 15. The polymer ofclaim 9, where the living polymer with one living end has a molecularweight from about 1 to 3 times the entanglement molecular weight, andwhere the living polymer with two living ends has a molecular weightfrom about 1 to 5 times the entanglement molecular weight.
 16. A methodfor making a comb-branched polymer, the method comprising: preparing amixture of living polymers that include living polymers with two livingends and living polymers with one living end to form a mixture of livingpolymers, and adding a coupling agent to the mixture of living polymers,where the coupling agent has at least three reactive functionalities.17. The method of claim 16, where the living polymers derive fromconjugated diene monomers and, optionally, vinyl aromatic monomers. 18.The method of claim 16, where the coupling agent has three reactivefunctionalities, and where after said step of adding a coupling agent,the molar ratio of living polymers with two living ends to livingpolymers with one living end to coupling agent is0.5-1.5:0.5-1.5:0.5-1.5.
 19. The method of claim 16, where the mixtureof living polymers is prepared in a solvent.
 20. The method of claim 16,where the living polymer with one living end has a molecular weight fromabout 0.25 to 10 times the entanglement molecular weight, and where theliving polymer with two living ends has a molecular weight from about0.25 to 20 times the entanglement molecular weight.